With increasing demand on high performance of electronic systems such as personal computers or electronic communication devices, operation speed and memory capacity of semiconductor memory devices such as DRAM are being improved. A semiconductor memory device mounted in a mobile system operated by a battery, such as a mobile phone or notebook computer, requires low power consumption. Therefore, much research is being actively conducted on a method for reducing an operating current and a standby current.
A DRAM memory cell including one transistor and one storage capacitor has a temperature-sensitive data retention characteristic. Therefore, an operation condition of circuit blocks within a semiconductor integrated circuit needs to be controlled according to a variation of the surrounding temperature. For example, DRAM used in mobile products controls a refresh period according to a variation of the surrounding temperature. In order to control such an operation condition depending on the variation of the surrounding temperature, a temperature sensor such as a digital temp sensor regulator (DTSR) or analog temp sensor regulator (ATSR) may be used. Such a temperature sensor serves to sense a high temperature, thereby controlling an operation period so as to reduce current consumption in a self refresh mode and monitoring the surrounding temperature during a normal operation.